Rail fasteners of the general type described above have heretofore been proposed: see e.g., German Auselgeschrift No. 1204697 and U.S. Pat. No. 3,576,293. The assemblies of each of the foregoing references include vertically extending flanges provided adjacent the opposite lateral edges of the lower plate for the purpose of limiting the extent of lateral movement of the rail-supporting upper plate of the assembly. Rail fastener assemblies of the aforesaid construction have not heretofore enjoyed widespread commercial acceptance. If the compression stiffness of the assemblies is sufficiently low as to provide the desired attenuation of the vertical shock and vibrations forces, the fastener assemblies do not perform satisfactorily under lateral or combined lateral and vertical loading. As is noted in U.S. Pat. No. 3,784,097, issued to the same assignee as above-discussed U.S. Pat. No. 3,576,293, lateral loading results in excessive deflection of the rail-supporting upper plate. Additionally, the magnitude of the lateral forces then imposed upon the upstanding flange of the bottom plate of the assembly can result in structural failure of such flange.